Method for feeding granular solids into metal melts

ABSTRACT

The invention relates to a method for feeding solids into metal or steel melts whereby granular solids required during the analysis adjustment are fed in a predetermined quantity into the turbulent regions of the metal melt in a dense flow process by means of a pneumatic conveying device in order to achieve a high output while avoiding expensive and complex measures associated with lances and capital-intensive investments for injection devices and lance-moving devices.

The invention relates to a method according to the Oberbegriff ofclaim 1. Through this method, solids which are added for the analysisadjustment during the metal production, in particular steel production,in varying amounts outside of the actual metal-producing process, can befed in a simple manner with a high accuracy in the analysis and a highoutput without using expensive auxiliary means like refractorilysupplied lances or threading machines to the metal melts.

K. Scheidig et al discloses in “Stahl und Eisen” (Steel and Iron),Volume 105, No. 25-26 of Dec. 16, 1985, Pages 1437-1441, a pneumaticinjecting of coal dust through the blast tuyere of a blast furnace bydense flow conveyance. The coal dust is thereby injected into the meltin measured quantities.

DE-OS 24 08 363 discloses a method for introducing finely dividedparticles of an aggregate into a liquid metal melt, while the melt isremoved from the melt container.

Because of the increasing demands by the customers regarding themaintaining of analysis regulations by the steel producer andsimultaneously continuously increasing competitive pressures, secondarymetallurgy, that is the treatment of the liquid metals following theactual metal production in a converter or electric-arc oven, hasincreasingly gained in importance within the past years. During thecourse of this development the method, through which fine-granular,fluid solids, as they are needed for adjusting the end analysis of theliquid metal, in particular, steel in varying amounts, are added to themetal melt, receive more and more importance with regard to theprediction of the output, the accuracy of the analysis, method expenses,operation safety and flexibility.

The methods, which are used today, are:

a) addition utilizing the force of gravity during the tapping by meansof sliding, flowing or manual feeding;

b) addition to the bath surface in the pan by means of conveyor systemsor manually;

c) threading of fill wires by means of threading machines;

d) injection by dipping in refractorily supplied dipping lances such as,for example, the TN-method.

The addition methods mentioned under a) and b) are characterized by notbeing exactly predictable, a comparatively low output and insufficientaccuracy, which results in the necessity of an increased consumption ofalloy media and, relatively often, a one-time or repeated correction ofthe added amount. If the addition is done manually, then additionalpersonnel are needed and, at the same time, the degree of thereproducibility of the analysis results is then comparatively even less.

By comparison, the methods mentioned under c) and d) are distinguishedby a comparatively high accuracy and high reproducibility. However, thehigh costs are disadvantageous.

These high costs are caused in the methods according to c) by theproduction costs of the fill wire needed for the threading, in themethods according to d) by the specific refractory costs of theinjection lances, which have a much shorter life because of the existingtemperatures and the necessary treatment duration than, for example, thepure flushing lances.

The injection methods are moreover characterized by expensive,personnel-intensive lance procedures.

Further disadvantages of the up to now used methods are that the amountsof alloy media, which can be added per unit of time, are limited by thetechnical boundary conditions, for example, during threading orinjecting. In addition, the metal melt experiences during the treatmentaccording to the method according to c) and d) a stronger cooling off,when threading in fill wires, it is necessary to additionally melt thesurrounding metal envelope and during injection, heat is additionallyradiated to the refractory material of the lance and to the transportgas.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE illustrates the injection of materials into a melt accordingto a process of the present invention.

The purpose of the invention is to design a method of the abovementionedtype in such a manner that with said method, fluid loose materials,which must be added in a suitable manner during the metal production, inparticular the steel production, following the actual melting process inthe converter or in the electric-arc oven for the correction of theanalysis of the metal, are added in a simple manner to the liquid metalso that a high utilization of the ratio between the amount absorbed bythe metal and the amount added is achieved without using expensiveauxiliary devices such as, for example, refractorily supplied lances,lance-moving devices, threading machines and by avoiding the use of fillwires.

This purpose is attained according to the invention with thecharacteristics of claim 1. The injection can occur into the tappingbeam of a converter or electric-arc oven utilized for the steelproduction during the tapping or into the impact area of the tappingbeam of a converter or of an electric-arc oven in the casting ladle orduring the ladle-metallurgical treatment following the melting processinto the area of the flushing spot during the flushing treatment on thebath surface.

Fluid loose materials, as they are usually utilized during the metalproduction for analysis adjustment, are, for example carbonaceousmaterials for carburization, lead, aluminum, sulfur, ferroalloys, andothers.

A condition for the use of the method of the invention is that thesematerials exist in a granular, injectable form. The grain size isthereby variable within certain limits but should, however, lie as muchas possible below 3 mm in diameter for reasons of a quick dissolving ofthe materials in the metal.

The loose material is injected by means of a pneumatically operatinginjection system, for example, according to EP 0 164 436. The size ofthe pressure receptacle of the system depends essentially on the size ofthe production unit and is related to the amount of material to beinjected per treatment. Usually a pressure receptacle with a 1,000 to2,000 1 capacity is used.

The loose materials to be injected can be supplied either through aclosed system in silo trucks and storage silos on site, through bigbags, sacks or smaller transport containers with a 1,000 or 1,500 1capacity. One or more intermediate receptacles are usually providedabove the pressure receptacle as day bunkers in order to assure a quickfilling of the injector after the end of the treatment.

The method of the invention, in addition, also provides the simultaneousor sequential addition of several different materials during the courseof one treatment.

The filing process and the following pressure build-up in the injectorare for this purpose automatically designed in such a manner that theinjector is again ready to convey within the shortest period of time.

Thus, smaller amounts of various materials can either be addedseparately, timely stepped or can be removed by preselecting the fillamounts one after the other into the injector and can be injected in onesingle operating step.

The materials are added into the melt by means of injection through alance 7, 8 and since the lance does not dip into the melt or comes intocontact with same, simple steel pipes without coating are sufficient aslances. Wear hardly occurs and the lances can be used again as often asdesired.

The place and the time of the addition can either be the clusteredtapping beam 3 of the liquid metal during the tapping, the impact area 9of the metal during the tapping in the ladle 4 or the flushing spot 6 onthe bath surface 5 during the ladle treatment.

The injection lances 7, 8 are for this purpose positioned by means of adevice of the method during the injection process in such a manner thatat all times the same boundary conditions like distance from the bathsurface, position on the bath surface, angle of inclination, etc. can bemaintained.

It is thereby important that even when the bath level 5 changes, forexample during the tapping process from an oven 1, at varying steelamounts 2 in the ladle 4 or caused by refractory wear, the optimumdistance of the lance top from the bath surface 5 is safely maintained.The method utilizes thereby already existing measuring methods, forexample, on the basis of a laser measurement, of ultrasoundmeasurements, etc.

When adding into the tapping beam 3, a high injection rate must beutilized since this operation is limited in time. Usual tapping times ofconverters 1 lie between 5 to 7 minutes and of electric-arc ovens witheccentric bottom tapping at approximately 2 minutes.

In order to guarantee the carrying along of the injected solids by thetapping beam into the metal amount already tapped into the ladle or inthe flushing spot area through the circulating effect into deeperregions of the metal melt, it is necessary to convey the solids in adense flow. Suitable injectors are available for this.

By means of the dense-flow conveying, it is guaranteed that the streamof solids hits in a clustered form either the tapping beam 3, the impactarea 9 of the tapping beam in the ladle or the flushing spot 6 duringtreatment in the ladle and the clustering of the stream of solids isthereby also still maintained at a distance of up to one meter from theend of the lance.

Thus, it is possible on the one hand to maintain the necessary distanceof the lances 7, 8 from the liquid metal in order to protect the lances7, 8 from wear and, on the other hand, the necessary precise working inthe area of the tapping beam 3 or of the flushing spot 6 is needed onlyin this manner as the condition for a high output rate.

In addition, using the dense-stream conveying makes it possible to workwith the least possible amounts of conveying gases. The method providesfor the utilization of all gases known in the area of themetal-producing industry like argon, nitrogen, air or even carbondioxide.

The advantages of the new method are that because of the dense-streamconveying, the costs for the transport gas are kept low, for example,when using argon or nitrogen, it is assured because of the smalltransport-gas amounts and the high conveying rate that no significantinfluence of the quality of the metal through the change of the nitrogencontent of the liquid melt occurs.

When the solid material needed for the analysis adjustment is injectedin the area of the flushing spot 6, then the absorption speed of theliquid metal for the injected solids does not only depend on the puredissolving power of the melt for, for example, carbon or silicon, but isyet significantly reinforced through the mechanical effect of impactingthe stream of solids in the area of the flushing spot in cooperationwith the circulating effect.

Thus, it is assured that the injected solids during the moment of impacton the bath surface 5 are immediately, that is, without delay, eitherdissolved in the bath or transported deep into the inside of the meltwhere the dissolving power for the injected solid material has not yetbeen exhausted.

The distribution of the injected solid material and thus theconcentration balance is effected by the circulating action of theflushing gas 10 introduced at the bottom. The homogeneity of the melt isthus guaranteed by means of a precise and regulated injection on the onehand and by the cooperation of the blowing impulse and circulatingaction on the other hand.

When the solids are injected into a tapping beam 3, then the carryingaction of the clustered metal stream takes care of the transport of alsolarge amounts of solids per unit of time into the already tapped amountof melt existing below in the ladle.

The angle, at which the stream of solids hits the tapping beam, shouldlie between 10 and 80°.

The method of the invention provides to couple computer-control of themovement of the injecting lance with the tipping movement of theconverter or of the electric-arc oven 1 in order to assure that thetapping beam 3 and the injected stream hit centrally onto one anotherwhen the solids are supposed to be blown into the tapping beam.

When the solids are supposed to be blown into the impact area 9 of thetapping beam during the tapping, then the injection lance must be liftedcorresponding with the rise of the bath level. This process can becontrolled by means of coupling the respective final control element onthe lance-moving device with the weighing system of the ladle carriageor other measuring systems for the weight detection. Also, a measuringof the bath-level height in the ladle is provided in the aforedescribedmanner.

When the solids are blown in the area of the flushing spot 6 onto thebath surface during the ladle treatment, it has been proven advantageousto arrange the injection lance 7 vertically. This simplifies thepositioning of the lance during the changing level of the bath surface5. A condition for this is that the geometric arrangement of theflushing system in the ladle bottom is maintained.

The applications relate to the injection of a fine-granular carbonaceousmaterial with approximately 88% C into the flushing-spot area of acasting ladle with 180 t tapping weight. It has been proven hereby thatoutputs of up to 300 kg/min carbonaceous material with a simultaneousgood utilization, here as output in relationship to the increase of thecarbon contents, can be achieved without any problems.

Also, the distance of the injection lance from the bath surface can bevaried in wide ranges. Even in the case of a distance of up to one meterfrom the bath surface, a high utilization is assured.

It has been proven to be advantageous to continue to flush the ladle 4after the treatment has ended. The melt is homogenized in this mannerand carbon particles, which have not yet been dissolved, and which hadalready been transported to the inside of the bath by the circulatingaction of the flushing gas and the mechanical impulse of the injectionstream, are dissolved in the melt. A further increase of the analyzedcarbon content is connected therewith.

What is claimed is:
 1. A method for introducing granular solids neededfor metal manufacture into a metal melt following a melt process bymeans of a pneumatic conveying system having at least one lance with anoutlet opening provided above the metal melt, characterized in that thegranular solids are transported by a conveying gas in the form of aclustered stream through turbulent areas into deep areas of the meltinto a tapping beam provided in the melt of a converter or of anelectric-arc oven utilized for steel production during tapping.
 2. Themethod according to claim 1, characterized in that the solids areinjected by means of a simple steel pipe, the diameter of which liesbetween ½″ and up to a maximum of 3″.
 3. The method according to claim1, characterized in that the distance of the injection lance from themelt surface or from a tapping beam provided in the melt lies between0.01 and 2.0 m.
 4. The method according to claim 1, characterized inthat argon, nitrogen, carbon dioxide or compressed air is used as aconveying gas.
 5. The method according to claim 1, characterized in thatthe grain size of the injected solids is less than 10 mm.
 6. The methodaccording to claim 1, characterized in that several different solids areinjected separately one after the other in several treatment steps. 7.The method according to claim 1, characterized in that several differentsolids are injected together in one treatment step.
 8. The methodaccording to claim 1, characterized in that the solids are injected by asimple steel pipe having a diameter of from 1 to 2″.
 9. The methodaccording to claim 1, characterized in that the distance of theinjection lance from the melt or from a tapping beam provided in themelt is from 0.1 to 1.00 m.
 10. The method according to claim 1,characterized in that the grain size of the injected solids is less than3 mm.
 11. The method according to claim 1, wherein the turbulent areasare formed by a scavenging area or at the surface of the melt at whichthe clustered stream impacts.
 12. A method for introducing granularsolids needed for metal manufacture into a metal melt following a meltprocess by means of a pneumatic conveying system having at least onelance with an outlet opening provided above the metal melt,characterized in that the granular solids are transported by a conveyinggas in the form of a clustered stream through turbulent areas into deepareas of the melt into an impact area of a tapping provided in the meltof a converter or of an electric-arc oven in a casting ladle.
 13. Themethod according to claim 12, characterized in that the solids areinjected by means of a simple steel pipe, the diameter of which liesbetween ½″ and up to a maximum of 3″.
 14. The method according to claim12, characterized in that the distance of the injection lance from themelt surface or from a tapping beam provided in the melt lies between0.01 and 2.0 m.
 15. The method according to claim 12, characterized inthat argon, nitrogen, carbon dioxide or compressed air is used as aconveying gas.
 16. The method according to claim 12, characterized inthat the grain size of the injected solids is less than 10 mm.
 17. Themethod according to claim 12, characterized in that several differentsolids are injected separately one after the other in several treatmentsteps.
 18. The method according to claim 12, characterized in thatseveral different solids are injected together in one treatment step.19. The method according to claim 12, characterized in that the solidsare injected by a simple steel pipe having a diameter of from 1 to 2″.20. The method according to claim 12, characterized in that the distanceof the injection lance from the melt or from a tapping beam provided inthe melt is from 0.1 to 1.00 m.
 21. The method according to claim 12,characterized in that the grain size of the injected solids is less than3 mm.
 22. The method according to claim 12, wherein the turbulent areasare formed by a scavenging area or at the surface of the melt at whichthe clustered stream impacts.
 23. A method for introducing granularsolids needed for metal manufacture into a metal melt following a meltprocess by means of a pneumatic conveying system having at least onelance with an outlet opening provided above the metal melt,characterized in that the granular solids are transported by a conveyinggas in the form of a clustered stream through turbulent areas into deepareas of the melt during a ladle-metallurgical treatment following themelt process in the area of a flushing spot during a flushing treatment.24. The method according to claim 23, characterized in that the solidsare injected by means of a simple steel pipe, the diameter of which liesbetween ½″ and up to a maximum of 3″.
 25. The method according to claim23, characterized in that the distance of the injection lance from themelt surface or from a tapping beam provided in the melt lies between0.01 and 2.0 m.
 26. The method according to claim 23, characterized inthat argon, nitrogen, carbon dioxide or compressed air is used as aconveying gas.
 27. The method according to claim 23, characterized inthat the grain size of the injected solids is less than 10 mm.
 28. Themethod according to claim 23, characterized in that several differentsolids are injected separately one after the other in several treatmentsteps.
 29. The method according to claim 23, characterized in thatseveral different solids are injected together in one treatment step.30. The method according to claim 23, characterized in that the solidsare injected by a simple steel pipe having a diameter of from 1 to 2″.31. The method according to claim 23, characterized in that the distanceof the injection lance from the melt or from a tapping beam provided inthe melt is from 0.1 to 1.00 m.
 32. The method according to claim 23,characterized in that the grain size of the injected solids is less than3 mm.
 33. The method according to claim 23, wherein the turbulent areasare formed by a scavenging area or at the surface of the melt at whichthe clustered stream impacts.